Abstract

A battery charging system for multiple series connected battery cells which includes a plurality of shunt regulators, adapted to be connected in parallel with each of the cells. The voltage of each cell is monitored during charging. When a cell is fully charged, excess charging current is shunted around the fully charged cell to enable the remaining cells to continue to charge. Circuitry is also provided to prevent the charging system from discharging the cells when the battery is not being charged. In an alternative battery charging system, a voltage source is connected across each of the serially connected batteries. Each voltage source is capable of sourcing or sending charging current. During charging conditions, the voltage sources source charging current to the cells. In order to prevent fully charged cells from being overcharged, the voltage across each cell is monitored. When the cell becomes fully charged, as indicated by the cell voltage, excess charging current is sunk to ground. In another embodiment of the invention, a rechargeable battery, formed from multiple internally series connected cells is provided with an integral battery charger within the battery housing.